This invention relates generally to pneumatic braking systems such as used on trucks and trailers and more particularly to a pneumatic brake booster incorporating an emergency fail safe mechanism.
A typical brake booster, as shown for example in U.S. Pat. No. 3291004, includes a housing having an actuator rod for coupling to the vehicle brakes. The booster incorporates a heavy duty diaphragm for moving the actuator rod in response to pressurized air received on one side of the diaphragm. The actuator rod is resiliently positioned against the opposite side of the diaphragm so that when the diaphragm is moved in response to pressurized air the actuator rod will actuate the brake drums and when the pressurized air is exhausted the actuator rod will release the brake drums. The housing further includes a second or emergency chamber disposed to the rear of the booster. The second chamber incorporates a second heavy duty diaphragm to the rear of which there is disposed a powerful emergency spring. An emergency rod is disposed between the first and second diaphragm such that when the powerful emergency spring is released the emergency rod urges the first diaphragm forwardly and thus actuates the actuator rod to set the brakes. The emergency spring is only released to set the brakes in the event that the pressurized air is deliberately released to set the brakes in a park mode or in the event of inadvertent loss of air pressure in the forward portion of the second chamber such as might result from a leak in the pneumatic line or failure of the compressor to operate. Whereas a booster of this type is generally satisfactory the known designs of this type are relatively heavy and relatively costly to produce.